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| *''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine | | *''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine |
| *Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species | | *Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species |
− | *''E. coli'' may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes dysentery | + | *''E. coli'' may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes [[General Pathology - Haemorrhage|Dysentery|dysentery]] |
− | *Enterotoxigenic ''E. coli'' (ETEC): | + | *'''Enterotoxigenic ''E. coli'' (ETEC)''': |
| **General: | | **General: |
| *** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis | | *** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis |
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| ***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs | | ***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs |
| ***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens) | | ***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens) |
− | ***The fimbriae are encoded by plasmids | + | ***The '''fimbriae are encoded by plasmids''' |
| ***These strains carry a plasmid which encodes an enterotoxin | | ***These strains carry a plasmid which encodes an enterotoxin |
− | ***Two types of enterotoxin: heat-labile (LT) and heat-stable (ST) toxins | + | ***Two types of '''enterotoxin: heat-labile (LT) and heat-stable (ST) toxins''' |
− | ***The plasmids which produce these toxins are responsible for the pathogenicity of these strains | + | ***The '''plasmids''' which produce these toxins are '''responsible for the pathogenicity''' of these strains |
− | ***LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer) | + | ****'''LT''' |
− | ***It attaches to the brush border of the epithelial cells of the small intestine | + | *****An oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer) |
− | ***LT causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes | + | *****It attaches to the brush border of the epithelial cells of the small intestine |
− | ***This causes irreversible activation of adenylate cyclase in target cells | + | *****Causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes |
− | ***This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium | + | *****This causes irreversible activation of adenylate cyclase in target cells |
− | ***ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion | + | *****This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium |
| + | ****'''ST''' |
| + | *****Activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion |
| **Clinical signs: | | **Clinical signs: |
| ***The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results | | ***The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results |